What is the reason for the failure of AD B2C sign-in after signing up through an email invitation?

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There could be various reasons for the failure of AD B2C sign-in after signing up through an email invitation, including:

1. Incorrect login credentials - The user might be using wrong username or password during the sign-in process.
2. Expired invitation - The email invitation may have expired, and the user needs to request a new invitation.
3. Email not verified - The user may not have verified their email address, which can cause issues during sign-in.
4. Technical issues - The AD B2C service may experience technical problems, causing sign-in failure for some users.
5. Permission issue - The user might not have the required permissions or access to sign in to the AD B2C service.